Acceleration Effects on Manual Performance With Isometric and Displacement Joysticks

Guardiera S, Bock O, Pongratz H, Krause W. Acceleration effects on manual performance with isometric and displacement joysticks. Aviat Space Environ Med 2007; 78:990–4. Background: We have shown before that novice human subjects produce exaggerated isometric forces when exposed to three times normal terrestrial acceleration (+3 G_z), and that this deficit is compensated by intensive training in +3 G_z. We now investigate whether training in normal terrestrial gravity (normal G) is also effective. We further examine whether subjects in +3 G_z produce not only exaggerated forces, but also exaggerated hand displacements. Methods: Experiments were conducted in the stationary (normal G) or rotating (+3 G_z) gondola of a man-rated centrifuge. With their dominant hand, subjects produced either forces using an isometric joystick, or hand displacements using a regular joystick. Response directions and magnitudes were prescribed visually. In practice trials, subjects received continuous visual feedback about their performance, while in test trials they did not. Results: Subjects produced exaggerated forces in +3 G_z, whether or not they previously practiced the task in normal G. In contrast, subjects did not produce exaggerated hand displacements in +3 G_z. Discussion: Exaggerated force production in +3 G_z is not overcome by task practice in normal G, as opposed to task practice in +3 G_z. This might be an indication that pilot training should contain extended practice of force production during phases of increased gravity (+G_z) to avoid motor deficits during flight maneuvers inducing +G_z. Furthermore, the control of isometric and regular joysticks seems to be based on partly distinct neural mechanisms, with different +G_z dependence. Thus, against the background of motor performance during +G_z, regular sticks might be favorably compared to isometric sticks in high-performance aircrafts.